Airtel audio engineer called me and told me that they are aware of this. He told me that Tata Sky is the reason for this decision from Airtel. He said that several customers have raised complaints saying Tata Sky is providing Dolby Digital Plus on many channels whereas Airtel is not providing it. So, they made a decision to just show the highest format supported by the Home Theater on all channels and content just to satisfy the users who raised such complaints. So, although the box is producing only 2 channel audio on stereo output, it fools the HT into thinking that it's receiving 5.1 channel input thus displaying the same. I also asked him about Amazon Prime not producing Dolby audio, and he said it must be raised with Amazon, as it's their app. He also said Netflix doesn't have such a problem on the box. If Amazon doesn't agree to resolve it from their end, he asked me to raise a complaint with Airtel and they will look into both the issues.
Probably it is not the right way of doing the thing. The box should have send the audio in it bitstream format (by disabling box system sound) and your HT should have processed to the desired way.
In your case, I am not sure whether the Xstream box is first converting the original 2 stereo channels into 5.1 Dolby Channels by simply padding 3.1 muted/ dummy channels into it and then converting it into PCM DTS or converting original 2 channels stereo audio into PCM DTS directly. The former will again be useless, the later will be useful to an extent.
As per Siva, enabling/disabling System sounds doesn't make change,...then what is this option meant for?
Airtel has deployed a bunch of nonprofessionals rather jokers.
I am not sure whether Airtel is working on for bringing back favourite mode in DTH viewing by filering out Non-Favrourite Chennels in channel navigation by pressing left or right button.
TRAI has declared that it will introduce Set Top Box interoperability by the end of this year. As per the report, TRAI has confirmed that the STB interoperability will be implemented by the end of 2019. I hope Reputed brand like samsung or Sony etc. lunches good Set UP Boxes.